1. Field of the Invention
The present invention relates to a regenerator for PCM signals represented in the AMI code with a time decision device having two clocked D flip-flops, at the output of which two separate unipolar pulse trains can be obtained which are regenerated with respect to amplitude and time, and having a code rule violation checking device.
2. Description of the Prior Art
The combination of a plurality of digitized speech signals and/or data signals to form a t.d.m. signal and the combination of a plurality of such t.d.m. signals finally results, across a plurality of hierarchy stages, in t.d.m. signals having bit rates which amount to a few hundred Mbit/s. Such t.d.m. signals are transmitted as pseudo-ternary digital signals across copper cables because of the freedom of the transmission signal from d.c., where the use of the AMI code frequently involves advantages. The AMI code is a pseudo-ternary code in which binary "0" digits are transmitted as zero elements and binary "1" digits are transmitted alternately as positive and negative signals having a logic "1" level, where the plurality of the consecutive "1" pulses in each case changes.
Within the transmission link, pulse regenerators are inserted at specific intervals in the cable link and in these regenerators the transmission signal is regenerated in respect of amplitude and time. During regeneration, because of the absence of a ternary logic, a first unipolar pulse train is produced from the positive "1" signals of the transmission signal and a second unipolar pulse train is produced from the negative "1" signals and the two pulse trains are regenerated separately in respect of amplitude and time. Then, it is possible to combine the unipolar pulse trains to form a new tranmission signal represented in the AMI code, and in the case of the end regenerator a different signal processing unit can be connected.
In accordance with the German published application No. 24 07 954, it is also possible to carry out the amplitude decision making process in comparators which are followed by the D flip-flops as time decision devices. Another possibility of making a direct decision as regards the bipolar AMI signal is that the D flip-flops--possibly preceded by amplitude filters--are matched to the signal level merely by a d.c. voltage level shift as regards the position of their thresholds. In this case, separate unipolar pulse trains occur at flip-flop outputs, which pulse trains must subsequently be combined.
As regards a simple possibility of producing an AMI signal by means of a quarter-wave tap line short-circuited at the end, it is desirable to convert the unipolar pulse trains into a signal represented in the binary-difference code in the regenerator. The code rule for this code consists in that a logic "1" in the binary input signal is marked as a change in the logic level from zero to one or from one to zero in the binary-difference code, whereas the logic "0" in the binary input signal is marked as the retention of the logic level one or zero from the previous bit in the binary-difference code.
The operational monitoring of such digital transmission systems with transmission signals represented in the AMI code employs the redundancy of this code which possesses three digital values, two of which, however, are used for the same state of the original signal for the information transmission. Employing the special property of the AMI code that consecutive one pules must always occur with a different polarity, by means of a code rule violation checking device it is possible to monitor the transmission signal even following scrambling with pseudo-random sequence. However, because of the conversion of the transmission signal in each individual intermediate regenerator, a code rule violation checking process is required in each individual intermediate regenerator.